1. Field of the Invention
This invention relates to a spinnerette for splitting a stream of molten polymer into a plurality of fibers as the polymer is extruded through a capillary of the spinnerette. This invention also relates to methods of making polymeric fibers, to polymeric fibers, and to nonwoven articles made from polymeric fibers. More specifically, the fibers of the present invention are capable of providing soft feeling nonwoven materials that have adequate tensile strength. The present invention also relates to fibers that are self-crimping, and which can also be subjected to mechanical crimping.
2. Discussion of Background Information
Nonwoven fabrics, which are used in products such as diapers, involve cloth produced from a preferably random arrangement or matting of natural and/or synthetic fibers held together by adhesives, heat and pressure, or needling. Nonwoven fabrics can be produced in various processes, such as by being spunbonded or cardbonded.
In the production of spunbonded nonwoven fabrics, fibers leaving a spinnerette are collected as continuous fiber, and bounded to form the nonwoven fabric. In particular, in a spunbond process, the polymer is melted and mixed with other additives in an extruder, and the melted polymer is fed by a spin pump and extruded through spinnerettes that have a large number of capillaries. Air ducts located below the spinnerettes continuously attenuate and cool the filaments with conditioned air. Draw down occurs as the filaments are drawn over the working width of the filaments by a high-velocity low-pressure zone to a moving conveyor belt where the filaments are entangled. The entangled filaments are randomly laid down on a conveyor belt which carries the unbonded web for bonding, such as through a thermal calender. The bonded web is then wound into a roll.
In the production of cardbonded nonwoven fabrics, filaments are extruded from spinnerettes in a manner similar to the spunbonded process. The filaments are either wound or collected in a can and subsequently cut into staple form of short length ranging from 0.5 mm to 65 mm which are carded and then bonded together, e.g., by a calender having heating points, or by hot air, or by heating through the use of ultrasonic welding. For example, staple fibers can be converted into nonwoven fabrics using, for example, a carding machine, and the carded fabric can be thermally bonded.
Staple fiber production processes include the more common two-step xe2x80x9clong spinxe2x80x9d process and the newer one-step xe2x80x9cshort spinxe2x80x9d process. The long spin process involves a first step comprising the melt-extrusion of fibers at typical spinning speeds of 300 to 3000 meters per minute. In the case of polypropylene the spinning speeds usually range from 300 to 2,500 meters per minute (and up to 10,000 meters per minute for polyester and Nylon). The second step involved draw processing which is usually run at 50 to 300 meters per minute. In this process the fibers are drawn, crimped, and cut into staple fiber.
The one-step short spin process involves conversion from polymer to staple fibers in a single step where typical spinning speeds are in the range of 50 to 250 meters per minute or higher. The productivity of the one-step process is maintained despite its low process speed by the use of about 5 to 20 times the number of capillaries in the spinnerette compared to that typically used in the long spin process. For example, spinnerettes for a typical commercial xe2x80x9clong spinxe2x80x9d process include approximately 50-4,000, preferably approximately 2,000-3,500 capillaries, and spinnerettes for a typical commercial xe2x80x9cshort spinxe2x80x9d process include approximately 500 to 100,000 capillaries preferably about 25,000 to 70,000 capillaries. Typical temperatures for extrusion of the spin melt in these processes are about 250-325xc2x0 C. Moreover, for processes wherein bicomponent fibers are being produced, the numbers of capillaries refers to the number of filaments being extruded.
The short spin process for manufacture of polypropylene fiber is significantly different from the long spin process in terms of the quenching conditions needed for spin continuity. In the short spin process, with high capillary density spinnerettes spinning around 100 meters/minute, quench air velocity is required in the range of about 900 to 3,000 meters/minute to complete fiber quenching within one inch below the spinnerette face. To the contrary, in the long spin process, with spinning speeds of about 1,000-2,000 meters/minute or higher, a lower quench air velocity in the range of about 15 to 150 meters/minute, preferably about 65 to 150 meters/minute, can be used.
With the above production processes in mind, the most desirable fiber for nonwoven applications has properties which will give high fabric strength, soft touch, and uniform fabric formation. The fiber is often used to form nonwoven cover stock, which is typically used for hygiene products, such as a top sheet of a diaper. In such applications, one face or side of the cover stock material is placed in contact with a human body, for example, placed on the skin of a baby. Therefore, it is desirable that the face in contact with the human body exhibit softness.
Softness of the nonwoven material is particularly important to the ultimate consumer. Thus, products containing softer nonwovens would be more appealing, and thereby produce greater sales of the products, such as diapers including softer layers.
Recent advancement in spunbonded fabric technology has improved the uniformity and fabric strength of the spunbonded fabrics. In the nonwoven market, spunbonded fabrics are taking over a good portion of the cardbonded fabric market. Accordingly, there exists a need for improved cardbonded fabrics in the nonwoven materials market.
Still further, WO 01/11119 and Slack, Chemical Fibers International, Vol. 50, April 2000, pages 180-181, the disclosures of which are incorporated by reference herein in their entireties, disclose fibers having a fat C-shaped cross-section.
Although currently available technology is usually able to achieve the desired level of fabric bulkiness, strength and softness, currently available technology may not always be economical. Some ingredients may be prohibitively costly, and the production rate may be too low to be economical. Also, it is known that fabric strength and softness can be increased if a finer fiber is used in constructing the nonwoven fabric. Many hygiene products currently in production have spin denier ranging from 2.0 to 4.0 dpf. The production of finer fiber, however, usually involves reduced production rates. Accordingly, there exists a need for improved fibers for either spunbonded or cardbonded fabrics which are economical to manufacture.
The present invention relates to the production of fibers, preferably fine denier fibers.
The present invention relates to the production of fibers, preferably fine denier fibers, at high production rates.
The present invention relates to stressing extruding polymer at an exit of a capillary to divide a fiber into a plurality of fibers.
The present invention relates to stressing extruding polymer at an exit of a capillary to affect the cross-sectional shape of the fiber.
The present invention also relates to providing a spinnerette for splitting a stream of molten polymer into a plurality of fibers as the polymer extruded through the spinnerette.
The present invention also relates to providing a differential stress to the extruding polymer at an exit of capillaries in the spinnerette to affect the cross-sectional shape of the fiber.
The present invention also relates to providing self-crimping fibers which may be used with or without mechanical crimping.
The present invention also relates to providing fibers with and without a skin-core structure. For example, the hot extrudate can be extruded at a high enough polymer temperature in an oxidative atmosphere under conditions to form a skin-core structure.
The present invention also relates to providing fibers for making nonwoven fabrics, such as cardbonded or spunbonded nonwoven fabrics.
The present invention also relates to providing thermal bonding fibers for making fabrics, especially with high softness, cross-directional strength, elongation, and toughness.
The present invention also relates to providing lower basis weight nonwoven materials that have strength properties, such as cross-directional strength, elongation and toughness that can be equal to or greater than these strength properties obtained with fibers at higher basis weights made under the same conditions.
The present invention also relates to providing fibers and nonwovens that can be handled on high speed machines, including high speed carding and bonding machines, that run at speeds as great as about 500 m/min.
The present invention relates to a spinnerette comprising a plate comprising a plurality of capillaries which have capillary ends with dividers which divide each capillary end into a plurality of openings.
The present invention also relates to a process of making polymeric fiber comprising passing a molten polymer through a spinnerette comprising a plurality of capillaries which have capillary ends with dividers which divide each capillary end into a plurality of openings so that the molten polymer is formed into separate polymeric fibers for each opening or the molten polymer is formed into partially split fiber for each capillary, and quenching the molten polymer to form polymeric fiber.
The plurality of capillaries can have a diameter of about 0.2 to about 1.3 mm.
The plurality of capillaries can comprise a capillary upper diameter which is less than a capillary lower diameter, and wherein a junction between the capillary upper diameter and the capillary lower diameter forms a ridge. The capillary lower diameter can be about 0.2 to about 1.3 mm. The capillary upper diameter can be about 0.6 to about 3.0 mm.
The ridge can comprise a ridge width of about 0.04 to about 0.8 mm.
The dividers can comprise a divider width which is about 0.1 to about 0.4 mm.
The spinnerette can further comprise a face having the plurality of openings, and wherein the dividers have divider ends which are flush with the face.
The dividers can comprise a divider height which is about 0.2 to about 2.0 mm.
The plurality of capillaries can comprise a ratio of a capillary upper diameter to a capillary lower diameter which is about 4:1 to about 1.5:1.
The plurality of openings comprise two, three, four or more openings.
The divider can have a tapered width.
The polymer preferably comprises polypropylene.
The polymer flow rate per capillary can be about 0.02 to about 0.9 gm/min/capillary.
The polymeric fiber can have a spun denier of about 0.5 to about 3.
The plurality of capillaries can have a diameter of about 0.2 to about 1.3 mm.
The spinnerette can be heated, such as electrically heated.
The polymeric fiber can have a substantially half-circular cross-section or a fat C-shaped cross section.
The polymeric fiber can be self-crimping, and the process can further comprise mechanically crimping of the polymeric fiber.
The polymeric fiber can comprise a skin-core polymeric fiber. Moreover, the polymer can be extruded in an oxidative atmosphere under conditions such that the polymeric fiber has a skin-core structure.
The present invention also relates to nonwoven materials comprising polymeric fiber made by the process of the present invention, to hygienic products comprising at least one absorbent layer, and at least one nonwoven fabric comprising fiber made by the process of the present invention thermally bonded together, and to polymeric fiber produced by the process of the present invention. The present invention also relates to wipes, which can be hydroentangled fibers of the present invention.